Combination tanning process



Patented Feb. 23, 1937' PATENT-Y OFFICE COMBINATION TANNING PROCESS George R. Pensel, Amsterdam, N. Y.

No Drawing.

Application April 13, 1935,

Serial No. 16,256

25 Claims.

This invention relates to the production of leather and more particularly to certain combi- .nation processes of tanning in which both metal and aldehyde tanning compounds are employed.

The general object of the invention is to providea novel tannage of this type whereby improved leathers may be obtained, with respect to texture, strength, and color.

Another object of the invention is to provide a combination tanning process of this character in which use is made of an organic salt, such'as an alkali metal salt of acetic, oxalic, lactic, tartaric, citric, and formic acids or the like as is referred to in my copending applications Serial Nos. 541,122 and 667,306 (now U. S. Patents Nos. 2,004,472 and 2,004,473) in connection with the so-called repickling or replacement steps de-- scribed therein.

' A further object of the invention resides in so controlling the pH value of the tanning bath at various stages of the combination'process that the full effectiveness of the several tanning in- I gredients is made available and lie-tanning is prevented.

Various combination tannages have been em-.

ployed in the past such as, for example, the following types: vegetable-chrome; vegetable-alum; vegetable-aldehyde; and various combinations of iron and other tannages'. Furthermore, formaldehyde has been employed, especially in connection with quinone, as a socalled pre-tannage for both chrome and vegetable tannages; However, by the novel processes disclosed in the present specification certain stated advantages have been obtained in the production of quality leather which have not been possible with these previous expedients. These processes are of special-importance in connection with the manufacture of fine glove leathers in which the utmost in ap pearance has to be maintained without sacrificing any-of the strength and durability. Glove leathers had been chiefly produced by chrome tanning which by itself produces a thin-fibered, somewhat empty leather of a distinct greenishbluish tinge, unless bleached by some after-treatment; or by an alum tannage which, while producing a plumper leather, is a veryweak tannage and the leather produced is not washable and will not stand a heat test.

Forthe purpose of emphasizing the practical differences and resulting advantages of the present combination processes over both the previ-' ous alum and chrome-tannages, as used in connection with the production of fine quality glove leather, ashort reference to these latter processes will be pertinent.

In most formulas for tanning with aluminium sulphate, the alum is made basic with an alkali and, of course, the tan is very unstable and gen- 5 erally washes out; in all cases it is necessary to -run the tannage over night and the relatively weak or ineffective tanning with the alum alone results in a tinny quality.

The French manufacturers make their alum glove leather by using a basic alum and piling away the skins for about six months for hydration. After this, the French skins are generally retanned with a small amount of chrome-alum and borax to render the alum tan more stable I! to washing and wear. Furthermore, in their subsequent fat liquoring process, the French manufacturers find it necessary to employ egg yolk, which is the common practice for alum tanned skins, and the resulting leather is not nearly as water resisting as that prepared in the present process and fat liquored with the proper oils.

By comparison with these prior alum tannages, the combination tannages described herein, in which alum is employed-whether as aluminum sulphate, potash alum, ammonium alum, or chrome alum-the following favorable differences are seen. The aldehyde completes the tanning which is initiated by the alum, removes the tinny" nature of the leather clue to this in complete tanning and renders the leather capable of standing a boil. The use of the organic salt, referred to herein and in my prior applications, further strengthens the tannages, especially in the matter of controlling the pH number and renders it possible to produce a leather which stands at least 190'F., where formerly it was necessary to add a certain amount of chrome; for example, using the two bath chrome processes to bolster up the leather to stand the heat test. .It is unnecessary to run the combination tan overnight unless a very plump leather is desired. In the present process, furthermore, it is unnecessary to store the alum tanned glove leather for'h'ydration, and the entire tanning process is 'speeded up without sacrificing quality.

Referring now to the differences between the combined metal and aldehyde tannage provided by the present invention and the previous chrome tannages employed in making quality leatherespecially glove leather-itis found that not only is the strength of the grain of the leather increased but a white leather of particularly fine appearance is produced which it has not been possible to produce by other chrome processes in which the leather is quite blue. The present chrome aldehyde process has been recently found very effective in producing certain grades of light Spanish lambs for glove leather which could never have been used for the manufacture of ladies gloves because when they are cut to weight on the ordinary tannage, the grain breaks. 0n the other hand, it is impossible to tear the grain of the leather by manually pulling it when it has been tanned by the present combination process.

In carrying out the chrome aldehyde tannage, the pickled skins, of a pH value of approximately 2.0, are floated in a bath containing about 10%- 20% of sodium chloride, based on the pickled weight of the skins; and then from 1%-3% of chrome tan, preferably basic chromium sulphate, is added at substantially room temperature and preferably in several feeds spaced at short intervals. The batch has then a pH value of from 2.0-2.5. I Then between 8% and 10%. of sodium acetate," or an equivalent water soluble organic salt, and preferably also approximately 1% of 84% acetic acid, or its equivalent, previously dissolved in a minimum of water, is added in several successive feeds, also at substantially room temperature. The skins now have a pH number of from 4.0-5.0 and stand a heat test of 170 F. Next, from 1%-3% of bicarbonate of soda or equivalent alkali is gradually fed into the bath, raising the pH value from 4.5-5.5, the skins standing 190 F. Finally from 5%-10% formaldehyde and approximately 2% of sodium bicarbonate, or 3 of borax, are added and after a short time the temperature of the bath is raised -to from 120-160 F., and the skins have a pH value of from 5.0-6.0. The tannage at this point stands a boil. The skins are then washed, horsed overnight, floated and fat liquored.

If desired, the sodium acetate and acetic acid may be added to the pickled skins before the metal salt, as in the processes described in my prior applications to which reference has been made.

In carrying out the combined alum aldehyde tannage, to the pickled skins is added a solution containing from 3%-15% of iron free aluminum sulphate or the equivalent in other aluminum salts, and from 3%-6% common salt, and drummed at approximately room temperature. The skins may then stand overnight, especially if added plumpness is desired. Then from 8%-10% sodium acetate or equivalent water so]- uble organic salt is added at a very slightly elevated temperature, the pH value then being from 3.0-3.5. Next 7%-15% of an aldehyde, preferably formaldehyde, together with from 5%-8% of borax, is added and the drumming is continued for a short time at the same temperature. Then enough borax is gradually added to bring the pH value up to from 4.5-5.5. The skins are then washed cold, raised to -150 F. and then drained and again floated and fat liquored. Analysis proves conclusively that the alum does not wash out.

Selected specific examples of especially effective actual runs will now be given in each case; the percentages stated being based on the pickled weight of the skins:

1. Chrome aldehyde tamzage.A batch of pickled skins having a pH number of 2.1 was floated in a bath containing 15% of sodium chloride, and then 2%of basic chromium sulphate was fed into the bath in three separate feeds, 10 minutes apart, at 70 F. (pH 2.3skins stood F.) Then there was added 9% of sodium acetate and 1% f acetic acid 84%, previously dissolved in a little water--in three feeds, 10 minutes apart, at 70 F. (pH 4.5-stood F.) Then, in three feeds at 10 minute intervals, 2% of sodium bicarbonate was added (pH 4.9-stood F.) Then there was added 7% of formaldehyde and 2% of sodium bicarbonate. The drum was run one hour before turning on the heat and the bath was then brought up to 140 F., and the tanning continued until the entire run had consumed about three and one-half hours. Next the skins were washed well for approximately 30 minutes, the leather at this point standing a boil. The skins were horsed overnight and the next day were floated and fat liquored. It will be noted that in this example, the metallic tanning materials were applied directly to the pickled skins. If desired, for certain purposes, the sodium acetate could be added first.

II. Alum aldehyde tannage.-The pH number of the pickled skins was 2.1. To thebatch there was added 10% iron free aluminum sulphate and 15% of sodium chloride and the skins were drummed for one hour at 70 F. After standing overnight, there was added 9% of sodium acetate and they were drummed for 'one hour at 80 F. (pH 3.2). Then the bath was run another hour at 80 F. after the addition of 10% formaldehyde and 6% borax. Then 8% borax was gradually added which brought the pH up to 5.0-5.5. The skins were washed cold one hour and then at 130 F. for 15 minutes; then drainedvery low, whereupon they were floated and fat liquored. In this particular case, the skins were fat liquored at 120 for about 30 minutes with a combination of sulphonated oils and neats-foot' its indicated and within the scope of the invention as defined in the following claims. It will be also understood that, although the present invention is adapted particularly to the preparation of fine quality white glove leathers, it

may be employed in connection with the preparation of various types of leather of both equal and inferior grades, such as leathers which are to be colored for various purposes or employed in the manufacture of shoe uppers or in other fields, wherein extreme thinness, durability, and appearance are not quite so much a criterion as in the glove industry.

" Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A process for producing leather from skins which includes the following step, treating the pickled skins in a one-bath process with a metal tanning solution, sodium acetate, and an aldehyde tanning agent.'

2.'A process for producing leather from skins which includes the following steps, treating the pickled skins in a bath with a quantity of a metal tanning compound which is inadequate of itself to completely tan the skins, adding sodium acetate, and completing the tanning operation with formaldehyde.

operation with formaldehyde.

4. A process for producing leather from skins which includes the following steps, treating the skins with a metal tanning agent at a lower pH value than normally most efficient for effecting a complete tanning with such compounds, raising the pH number to the vicinity of 4.5-5.5, and

completing the tanning with an aldehyde tan pickled skins with a metal tanning agent, the.

skins then having a pH value of 1.8-2.5, adding sodium acetate to bring the pH value to 4.0-5.0, and completing the tanning operation with formaldehyde to a pH value of 4.5-6.0.

7,. A process for producing leather fromskins which includes the following steps, treating the pickled skins with a metal tanning agent, the skins then having a pH value of 2.0-2.5, adding sodium acetate to bring the pH number to approximately 4.5, and completing the tanning operation with formaldehyde to a pH value of approximately 5.5.-

8. 'A process for producing leather from skins which includes the following steps, treating the pickled skins with a chrome tanning compound at a lower pH .value than normally most efficient for a chrome tannage, and in a quantity insuflicient to completely tan the skins, raising the pH value to the vicinity of 4.5-5.5, and completing the tanning with formaldehyde.

9. A process for producing leatherfrom skins which includes the following steps, treating the pickled skins with a chrome tanning compound, adding sodium acetate, and then adding formaldehyde.

10. A process for producing leatherfrom skins which includes the following steps, treating the pickled skins with a-chrome tanning compound, adding a salt of a water soluble organic acid, selected from the following group: acetic, formic, oxalic, lactic, tartaric, and citric, andsthen adding formaldehyde.

11. A process for producing leather from skins which includes the following steps, treating the pickled skins with an aluminum tanning compound, adding sodium acetate, and then adding formaldehyde.

12. A process for producing leather from skins which includes the following steps, treating the pickled skins with an aluminum tanning compound, adding a salt of a water soluble organic acid, selected from thefollowing group: acetic, formic, oxalic, lactic, tartaric, and citric, and then adding formaldehyde.

13. A process for producing leather from skins which includes the following steps, treating the pickled skins with a water soluble salt of a soluble organic acid, selected from the following group: acetic, formic, oxalic, lactic, tartaric, and citric and subjecting them to a combined tannage of metal and aldehyde. I

14. A process for producing leather from skins which includes the following steps, treating the pickled skins with a water soluble-alkali salt of an organic acid, selected from the following group: acetic, formic, oxalic, lactic, tartaric, and

citric, and tanning in a one-bath process with a metallic compound and formaldehyde.

15. A process for producing leather from skins which includes the following steps, treating the pickledskins with a water soluble salt of an organic acid, selected from the following group: acetic, formic, oxalic, lactic, tartaric, and citric, togetherwith a quantity of the organic acid itself, then tanning with a metal tanning agent,

and analdehyde tanning agent.

'mately 2.0 and raising it during tanning to approximately 5.5gwhereby the skins are first partially chrome tanned, and'then finally completely tanned by the aldehyde.

17. A process for producing leather from skins which includes the following steps, floating the skins in a bath containing a quantity of sodium chloride, 1%-3% of a chrome tanning compound, then adding 8%-l0% sodium acetate, then a small quantity of alkali, and finally adding to the bath 5%-10% of formaldehyde and a small further quantity of alkali, said percentages being based upon the pickled weight of the skins.

18. A process for producing leather from skins which includes the following steps, floating the 1 skins in a bath containing a quantity of sodium 7% formaldehyde and a small further quantity of alkali, said percentages being based upon the pickled weight of the skins.

19. A process for producing leather from skins which includes the sfollowing' steps, floating the skins in a bath containing a quantity of sodium chloride, l%-3% of a chrome tanning compound, then adding 9% sodium acetate, 1% of 84% acetic acid, then a small quantity of alkali, and finally adding to the bath 5%10% of formaldehyde,

and a small further quantity of alkali, said percentages being based upon thepickled weight of the skins.

20. A process for producing leather from skins which includes the following steps, floating the pickled skins in a bath containing 15% of sodium chloride and gradually adding 2% of basic chromium sulphate in successive feeds over a period of approximately one-half hour, adding 9% of sodium acetate in successive feeds over a period of approximately one-half hour, then adding alkali equivalent to 2% of bicarbonate of soda in successive feeds over a period of about onehalf hour, then adding 7% of formaldehyde and 2% of bicarbonate of soda or its equivalent, allowing the bath to stand for one hour, then raising the temperature to 140 F., running the bath for approximately another hour at said elevated temperature, and finally washing and finishing the skins.

21. A process for producing leather from skins which includes the following steps, adding to the skins an alum tanning agent of the equivalent cf'aluminum sulphate in amount approximately of the pickled weight of the skins, adding approximately 9% of sodium acetate, then adding approximately 10% of formaldehyde together '80" F. and raising the pH value of the skins by the addition of borax or an equivalent alkali to gradually bring the pH value up to 5.04.5, and finally washing the skins at about F., draining and suitably finishing the skins.

23. In a combined metal and aldehyde tanning process, the step of adding to the bath in which the previously pickled skins are tanned, a quantity of a salt of a water soluble organic acid, selected from the following group: acetic, formic, oxalic, lactic, tartaric, and citric, in order to raise the pH value of said bath to points of optimum tanning efliciency of the metal and aldehyde ingredients respectively.

24. In a combined metal and aldehyde tanning process, the step of adding to the bath in which the previousLv pickled skins are tanned, a quantity of sodium acetate, in order to raise the pH value of said bath to points of optimum tanning efiiciency of the metal and aldehyde ingredients respectively.

25. In a combined metal and aldehyde tanning process, the step of adding to the bath in which the previously pickled skins are tanned, a quantity of a salt of a'water soluble organic acid selected from the following group: acetic, formic, oxalic, lactic, tartaric, and citric, together with a quantity of the organic acid itself, in orderto raise the pH value of said bath to points of optimum tanning efliciency of the metal and aldehyde ingredients respectively. 7

GEORGE R. PENSEL. 

